Gene acquisition is crucial for the evolution and emergence of pathogenic bacteria. Traits acquired by pathogens enable them to survive in their reservoirs, and colonize and injure the hosts that they infect. Shiga toxin-producing E. coli (STEC), such as E. coli 0157:H7 and selected non-0157:H7 toxin-producing E. coli, provide a unique opportunity to study the evolutionary aspect of the acquisition of virulence traits. E. coli containing genes encoding Shiga toxins are phylogenetically diverse, but virulent strains are almost always found in two well defined phylogenetic clusters (STEC 1 and STEC 2 groups). The investigators propose to study systematically, using comparative genome analysis, the traits these pathogens have acquired, to determine the distribution of putative virulence loci, and to discern the sequence of acquisition of these traits. They will also assess the clonal nature of gene expression of these pathogens in bovids and humans. Data generated by this project will elucidate the mechanisms used by virulent organisms to accumulate the necessary genetic components to be successful pathogens.